Consumers desire the ability to control many devices remotely in the modern world. Automatic garage door openers are one example of such devices. Automatic garage door openers are widely used to open and close garage doors. Automatic garage door openers include a transmitter and a receiver. The transmitter is a wireless remote device that includes a button. Upon activation of the button, the transmitter sends a garage door operation code to the receiver mounted within the garage. Upon receipt of the code, the receiver instructs a motor to open or close the garage door.
While garage door openers are convenient, there are times when homeowners and other users would like to open or close a garage door in the absence of the wireless transmitter for the garage door opener. For example, when a homeowner leaves the home and walks to a nearby location, he or she may prefer to enter by the garage upon his or her return. However, without the garage door opener transmitter, entry by the garage is prohibited unless the homeowner has installed a special exterior keypad transmitter. Another common situation is when the homeowner removes the wireless transmitter from his or her automobile for some reason and forgets to replace the transmitter before returning home. In such a case, a homeowner may have removed the wireless transmitter from his or her automobile and given the transmitter to a friend who needs access to the home. If the homeowner does not recover the wireless transmitter from the friend before returning home, he or she will be unable to enter the garage upon initially pulling up to the garage, as would be possible with the wireless transmitter. Accordingly, it would be desirable to provide an alternative transmitter allowing a user to operate an automatic garage door opener. It would also be desirable for the alternative transmitter to be provided on a device that is commonly used in association with automobiles and home entry in general, such that the homeowner typically carries the device on his or her person when away from the home.
Most automobiles today are sold with remote keyless entry (RKE) systems. For those automobiles not equipped with RKE systems, such systems may be purchased in the aftermarket. RKE systems generally include a wireless transmitter and a receiver located within the automobile. The wireless transmitter is commonly referred to as a key fob. The key fob is configured to hold a plurality of keys, such as keys on a key ring. The key fob may be separate from a key or may even be incorporated with a key as a single unit. In any event, the key fob typically includes one or more buttons that may be activated. Depression of one of the buttons on the key fob causes the wireless transmitter to transmit an automobile instruction signal associated with the button to the receiver within the vehicle. For example, depression of a door lock button on the key fob will result in transmission of a door lock instruction signal. Examples of other buttons having associated automobile instruction signals include trunk release buttons, unlock buttons, alarm buttons, panic buttons, and remote start buttons.
RKE systems use a particular government or industry designated frequency (or limited number of frequencies) to transmit their signals, which may vary from country to country. A general design challenge for RKE systems is to achieve low power consumption in both the RKE transmitter and receiver, while achieving good range and reliability for the RKE system.
Another design challenge for RKE systems is code security. When an RKE system transmits only a single or limited number of codes it is possible for a radio scanner to capture the code. Once the code is captured, a thief may retransmit the code to the automobile in order to gain access. Thus many modern RKE systems use a 40-bit rolling code to assist with security.
With a 40-bit rolling code approximately 1 trillion codes are available for a given instruction. The transmitter's controller chip has a memory location that holds a current 40-bit code. When a button on the key fob is pressed, it sends that 40-bit code along with an automobile instruction code that tells the car what to do (such as lock the doors or open the trunk). The receiver's controller chip also has a memory location that holds the current 40-bit code. If the receiver gets the 40-bit code it expects, then it performs the requested function. If not, the receiver does nothing. The key fob transmitter and the automobile receiver use equivalent pseudo-random number generators. When the transmitter sends a 40-bit code, it uses the pseudo-random number generator to pick a new code, which it stores in memory. On the other end, when the receiver receives a valid code, it uses the pseudo-random number generator to pick a new one. To avoid problems associated with lost transmissions, the receiver will accept any of a predetermined number of next possible codes (e.g., any of the next 256 possible valid codes).
Key fob owners typically also attach vehicle keys and home keys to the key fob. This means that the RKE key fob is typically carried by homeowner when leaving home, whether the homeowner leaves by vehicle or on foot. Thus, the RKE key fob presents unique opportunities for an alternative device that may be used as a garage door transmitter or other controller for any of numerous different devices that may be remotely controlled.